Summary update on BAAH-1, the L-1 cert bird. Okay, more than simply update: more of a recent history, since it’s now been quite some time since my last BAAH-1 posting. In fact, I started this update back in November 2014!

Construction at that time was mostly complete. The only things remaining were the avionics bay (it was built, but the contents were not laid out, attached, and wired), some shear pins (especially given the loose fit between the airframe and the avionics bay’s couplers), lettering, final attachment of the launch guides, and connecting up the parachute.

Unfortunately—though not too surprisingly, given the history of this rocket—it’s a bunch more massive than the original design and sims. Enough so that I need to change motors: it’s up to about 2650 grams. That’s what happens, though, when you go not just with Blue Tube, but also add a bunch of steel blind nuts and such for launch guide attachment. Certainly the balsa nose cone (instead of a hollow plastic one) doesn’t help overall mass, but at least I knew about that.

With the nose cone assembly and fin prep complete (see this post), there was still a bunch of building to do, such as attaching the fins. Relatively straightforward—see the picture to the right—though I filleted like crazy at all joints, inside and out, using 30-minute cure epoxy on the outside joints, JB Weld on the inside joints. More about the fin arrangement later.

It wasn’t too hard to take care of the mechanicals in the av bay. These included, though, static ports (and vent holes in the airframe), and, as noted, drilling and threading holes for the shear pins. The shear pins weren’t completely straightforward: despite using Blue Tube, I wanted to ensure a good cut on the pins, and good longevity for the airframe. So, I cut some brass shim stock, ground some depressions, and placed the shim stock beneath where the shear pins will go. This allows the brass to cut the pins and take the load, not the Blue Tube. You can see the laid-in but not yet drilled shear pin cutter below.

Shear Pin Cutter

Two other holes needed were for the master avionics switch and an LED to indicate master power to the avionics.

The last bits on the avionics bay were the final wiring to connectors, so I could assemble and disassemble the bay, along with placement and wiring of the ejection charge connectors on the outboard sides of the bulkheads. Again, nothing complicated.

Why all these avionics? I had plans to fly dual deployment, though the certification flight would be simpler: altimeter deployment, with motor deployment backup.

Nice red nose!

Painting was an interesting situation. I wasn’t just building any old rocket for my L-1 cert bird: BAAH-1 is a full-scale model of Auk XXXI, the last rocket that Homer Hickam and the Coalwood Rocket Boys flew. (But what about the Miss Riley, the last rocket flown as depicted in October Sky? According to an email conversation I had with Dr. Hickam in July 2000, there was no Miss Riley: their last rocket was simply the next in the Auk series, Auk XXXI. In that email exchange, I also got the details of Auk XXXI: diameter, height, materials, paint, and approximate fin size, planform, and arrangement. It’s on the information from this exchange that I built the rocket.) Auk XXXI was a steel tube with aluminum fins and a turned spruce nose cone, painted red (see picture at right). The tube and fins were unpainted, except for “BCMA” across the top and “Auk XXXI” down the face of the steel tube.

Dr. Hickam also explained how the fins were attached to the rocket. The fins were pieces of sheet aluminum, with the corners snipped. Each piece made up two fins, and was bent to conform to the rocket’s body and then stick out into the airstream. From the bottom of the rocket, they looked more like an X than like a +. So, that’s what I did, though with wood and slotted airframe, not bent sheet aluminum.

Body tubes ready for priming

To make the tubes look more like metal, I filled the spiral winds, then sanded. The picture on the left shows the upper and lower tubes filled, sanded, and ready for primer. With a little hunting, I found two different shades of silver-ish paint, the one I thought looked more like steel for the body, more like aluminum for the fins.

Flush-mounted Blind Nut

For initial launch guidance, the Rocket Boys used a launch rod in the ground and ¼” eye bolts on the rocket. Easy enough to model those: my Auk XXXI also has ¼” eye bolts for the initial flight guidance. At the right is one of the flush-mounted blind nuts used with the eye bolts. Though straightforward in concept, I wanted a truly flush mount, so that when primed and painted it look like it was simply a threaded hole in the side of the rocket. Using a grinding bit and a drill press, I ground out a depression on the airframe tube, then ground the blind nut’s base so it was thinner and bent the base to match the curvature of the tube. Some epoxy, and I was ready for primer.

Auk-XXXI Ready to Fly

My younger son did the lettering for me.

Auk-XXXI under canopy

Everything finally came together on December 6 (yes, 2014). The rocket was ready, LUNAR was cleared to launch at the Orvis‘s Snow Ranch, I had the motor and casings. Right. All except the last one. I had the casings, but not the right motor. Remember the rocket had grown heavier? That meant a late change in motors. Thanks to Mike at Bay Area Rocketry, I was able to get the right motor, an H-148R, at the launch, last minute.

Since December 2014, I’ve flown Auk XXXI a few more times, on different motors, including White Lightning (bright yellow flame with white smoke) and Black Max (dense black smoke). Here’s a launch sequence from January 2016.

April 4, 2015. It’s been a long time since then, but that’s when my AS-501 model flew.

Waaaaay back in March, I posted my previous AS-501 entry. In our last episode, we left the bird all in white. Here’s the reset of the story.

Masked for extra white

Black roll pattern painted

AS-501 is, in the true sense of the word, unique. For one thing, the S-IC left the factory with a different paint scheme than you see in the pictures of the bird on the pad. Those pictures show a roll pattern like every other Saturn V flight article. In fact, AS-501 originally had a roll pattern like that of AS-500F, the facilities checkout unit. (You can see a sample photo here. Notice the black roll pattern extends into and fully around the top of the intertank section.) This roll pattern had much more black paint. NASA realized that this paint absorbed more heat from the sun, which resulted in higher internal fuel tank temperatures, making it more difficult to keep the cryogenic oxygen cold. They painted over that roll pattern, and it looks, at more than first glance, to be the normal S-IC roll pattern. If you look very carefully, though, you’ll see that there’s a very slight shadow of the original black showing through the white over it. I tried to mimic that in my AS-501 model.

The masking and the painting and the unmasking and the masking and the painting and the unmasking continued. And continued. And continued. That’s the lot of a Saturn V modeler: that iconic roll pattern is an ever-present cursed bane.

If the S-IC and S-II roll pattern masking doesn’t drive you batty, just wait until it’s time to mask for the S-IVB’s antennas. At the right, you’ll see the S-IVB with its after interstage and the IU. The area with all those white squares near the top is actually reverse-masked, so I can apply some masking goo on just the antennas. I’ll peel away the masking tape leaving just the goo over just the antennas, then spray black. Masking some of the details that extend into the roll pattern (parts that should be white in an area painted black, like the retrorocket that’s masked in beige just extending below the blue tape on the left side of the picture, perhaps ⅓ of the way up) was also a challenge.

RCS quads painted

Fly-away umbilical plug background

On the left, you’ll see the RCS quads. They presented their own challenge—not so much because of the masking (none, really) or colors (though I wanted to match the sort of iridescent black one sees in an unflown RCS quad bell), but in the modeling. One of the RCS quads had a broken nozzle, requiring repair. If I look carefully, I can find the hand-crafted one. I’m not completely happy with how the paint flowed, but the paint flowed.

On the right is a detail of the masking and painting of one of the S-IVB’s fly-away umbilical panels (this is at Position II). Though the kit includes decals for some of these panels, it doesn’t include all of them. If I wanted to be accurate, I hand-painted these. First, mask. Then, paint the yellow. After the yellow’s dry, unmask, then paint some black dots (representing the plugs). Let that dry.

Fins showing cutting guides on the tabs

Three more steps remained. First, I had to reattach the fins. When originally built, the fins were attached. By the time this kit reached my hands, some of the finds had been broken off. One of the four fins was completely broken off, the other was broken part-way down. I decided that the best thing was to finish the job, break the second one off all the way down, and then replace both fins. As you can see in the picture on the left, the fins are through-the-wall affairs, with very deep tabs. Rather than trying to effect a surface mount repair, I decided to excavate out some of the tab (since fully extracting it was not feasible without inflicting more general damage on the rocket—e.g., to the fin and engine bell fairings), then carve the tab of the new fin to match the available space in the fin slot. In general, I pulled out more material than the remaining tab in the B fin, above (the fin to the left) would indicate, but I let the epoxy fill in those voids to add strength.

Lead in the CM

Once the fins dried, I found the parachutes I would use (the main chute from my L-1 cert project, and the drogue from the same project, as-yet unused, since I’ve only flown it single deployment), attached those and some parachute protectors, and put a full motor into the rocket. This let me determine the CG, to check stability. Not surprisingly, the CG was very far aft—too far aft of the CP for good stability. Time to add weight to the nose.

The available space for the weight was the command module. The clay provided with the kit was inadequate: there just wasn’t enough to balance the rocket. I had additional modelling clay available, but I checked its density and the volume of the space in the CM, and concluded that clay simply wasn’t dense enough to do the job. The only practical thing that would work would be lead. Lead shot, for example.

On the pad, ready to go!

Recovered!

I didn’t have any lead shot. Checking around, the stuff seemed expensive. I didn’t care how I got the lead, all I cared about was that it be in a form like lead shot: small balls. Thinking a bit, I realized that a soft scuba diving weight was just a nylon pouch filled with lead shot. I called a local dive shop, confirmed they had soft dive weights, stopped there on my way home from work, and had five pounds of lead shot for something like a couple dollars a pound. Not cheap, but also nowhere near as expensive as lead shot from a shooting store. I filled the CM mostly full, as you can see in the picture above, and mixed in some epoxy to hold things in place.

Post-flight, lower portion (S-IC, S-II)

It was time to fly.

On the left above is the rocket poised on the pad. It seemed a lot of rocket to launch off a rod, instead of a rail, but that’s how it was built before I got it. I thought about adding rail buttons, decided against it. AS-501 flew on a CTI H-100, clearing the tower at about 15 meters/second, reaching about 250 meters altitude. Thanks to a fellow rocketeer, I have a pretty nice ignition and launch sequence: rapid-fire burst of exposures starting just about as the H-100 was lighting, which you can see at the bottom of this blog post. As frequently happened with a composite motor, it took a little time for thrust to build, but not so long as to be of any real concern.

Then, the rocket started to move, climbing away on its flame front, up above the motor’s smoke.

Admittedly, AS-501 looked a little naked without the launch escape system topping the stack, and with just the bare CM there. But, the LES from this model needed a lot of repair work to make it usable, and I didn’t want to put the time into it before first flight—especially since I wanted to meet my commitment of flying the bird during that Snow Ranch launch season.

Post flight, upper portion (S-IVB, LSA, SM, CM)

As to the aftermath, take a look on the right above and on the left. Above right is the lower portion (the S-IC and S-II) as I found it in the grass. No damage at all. The parachute laid out very nicely, having lowered the rocket gently. Immediately to the left is a close-up of the landing. Position I is visible on the top side. Looks like a Fin D decal fell off somewhere along the way.

Hole punched in the LSA

To the right is the upper portion of the rocket (S-IVB, LSA, SM, and CM) as I found it. The picture tells the story of the landing: some drift, from the left of the frame, with the shock cord draping over the bush in the final stages of the descent.

Given the location of this recovery site, the bush probably saved some damage, It wouldn’t have been real good if the upper portion of the rocket had hit that large rock that’s just to the left of the image center. But, there was a little damage. It looks, from the picture at the left, as though the rocket either hit a branch as it landed, or it swung into the branch as it hung. It’s not a lot of damage, and the only thing that will make it hard to repair is trying to make it as invisible as possible.

In addition to other projects (Folie à Trois), I plan to repair the hole and launch AS-501 again this fall-winter Snow Ranch launch season.

It’s a another lunatic project. First, scratch-build my L-1 cert project (see these posts; yes, I finished the project, even though I’ve not written about the final build portions and flight: that will come). Then, repair and complete another 1:70 Saturn V, modeling AS-501 (aka Apollo 4), which has numerous differences from Apollo 11 (AS-505), the vehicle on which the model was based.

Now, scratch-build my first high-power cluster-capable rocket.

Not just any cluster. A sane first cluster project would be two motors, or three motors in a tight triangle. My first high-power cluster project has three motors inline, and will be capable of flying on one, two, or three motors. When it flies on three, it can be launched on one, two, or three motors through air-start capability. The rocket will also have dual deployment capability.

Two avionics bays, two computers. One computer will be used to control deployment, a second (either completely separate computer or a remote triggering device) to control in-flight motor ignition.

Sounds crazy, no? But, in our little village of Palo Alto…

Here’s the side view of the rocket design.

Base 29-100 Centering Ring

First Extra Hole Drilled

It’s a wholly conventional basic planform, 3FNC (three fins and a nosecone)—except for the fins, which have a bit of a flair to them.

After designing the rocket (using RockSim), I figured a good next step was to start on the motor mount assembly. This was going to be one of the most complicated parts of the rocket. At the left is one of the starting points for the motor mount: an unmodified 29-100 plywood centering ring. At the right is that same CR with the first of two extra in-line holes drilled. I drilled out the hole using a 1⅛” Forstner bit, which comes out to about 28.5mm. That’s as close to 29mm that I could find, especially without going larger than 29mm. (Yes, I looked around: not just locally, but in various shops online. I couldn’t find a 29mm Forstner bit, at least not without it being part of a large set—at best. I really wasn’t interested in spending $50 just to get that one bit I cared about.)

All MMT Holes Drilled and Sized

CR Template

The most important tools were my drill press, that Forstner bit, and the CR template from RockSim. With the template, it was easy to locate the centers of the two outboard MMT holes, since each has its center marked (see the image to the left). You can see that template in the image to the left. To the right, the CR with the three MMT holes drilled, and sized. I did the final sizing (enlarging the 1⅛” holes to 29mm) again using the drill press, this time with a cylindrical abrasive sanding bit: sand a little, test fit, sand a little, test fit… (Note the coordinate markings in the drilled CR. More holes will be drilled, and I wanted to keep the orientation correct, along with that of the motor mount assembly in the airframe. Aligning a three-abreast motor mount with three through-the-wall fin tabs isn’t trivial.)

Motor Mount Unglued

Blind Nuts Epoxied

MMT, Blind Nut, and Igniter Tunnel Holes Drilled

At left are the motor mount tubes and centering rings assembled for a test fit.

On the right, you’ll see the extra holes drilled in the aft CR. The two holes closest to the edge are for igniter wire tunnels. I’ll put an aluminum tube through each, to also run through identical holes in the mid CR. Igniter wire will then be able to run from the computer module in the aft avionics bay that will live between the forward and mid CRs, down to the motors for air start ignition.

The other six holes are for blind nuts (aka t-nuts), which I’ll use to hold the motor retainers in place. I plan to use window screen retainers fur the purpose: they’re inexpensive, light, and will fit given the motor layout (whereas something like an AeroPak retainer won’t fit). Further to the right right you’ll see those blind nuts epoxied in place.

Finally, time to start the real assembly of the MMT.

Fwd and Mid CRs Glued

U-Bolts Added

Left: the forward and mid CRs are epoxied in place (with JB Weld), and the aft CR is placed as a support. The aft CR will be attached after the motor mount and fins are installed, positioned flush against the aft edges of the TTW fin tabs.

I’m using a pair of u-bolts to attach the recovery harness to the forward CR. Though I’m sure this is gross overkill—two u-bolts instead of one, or instead of a single lifting bolt—the pair will help even out the forces on the rocket. In the picture on the right you can see the u-bolts attached. These will not need to be removed, so I used a high-strength thread locker to secure the nuts to the u-bolts.

Once everything dried, it was time to add the housing for the avionics bay. That housing—a tubing coupler—presented its own challenges. Not because of the housing or the design, but because of my implementation.

Avionics Bay Added

I put it on at the wrong time.

The centering rings are sized to fit into the airframe. So is the tubing coupler. In other words, the CR and the TC have the same diameters. Since the TC’s wall is about 1mm thick, the CRs are too big to fit inside the TC—by about 2mm. Once I decided how to handle this, it wasn’t a difficult problem to solve. With the help of a new belt sander, I reduced the diameter of the forward and mid CRs so the TC would fit. Then, it was a simple matter of epoxying everything together.

Next up: cutting the hatch (door) in the aft avionics bay. I plan to cut the hatch in the TC slightly smaller than that in the airframe and glue them together for a bit of extra strength.

A few months ago, one of the guys on the LUNAR club list, Paul, sent email offering a 1:70 scale Saturn V model. It was partially completed, and needed finishing. Paul realized he’d never finish it, and wanted to see it fly. It had been modified from the original 29 mm motor mount to use a 38 mm motor mount. The rocket was structurally complete, though two of the four fins were broken off, another was damaged, and there was damage to some of the vacu-formed wraps that add detail to the model. Another Club member, Tony, had done the original work on the construction, and it had sat at that point for a long time.

I agreed to finish it, and the general Club consensus was that I should.

Having built one of these before, and modeled Apollo 15 (AS-510), I decided I’d model Apollo 4 (AS-501) this time. It’s not a trivial task: AS-501 has some structural and paint differences from Apollo 11 (AS-506), on which the model and the finishing instructions were based.

Note the gap between the edges of the wrap. There are also cracks.

Repaired wrap gap and cracks.

Before starting the real work, repairs were in order. Left and right are before and after pictures of one such repair.

These wraps are finicky: getting them on in a way they’ll stick, without damaging them (cracking or melting from the adhesive) is difficult to begin with. If the wraps aren’t good and tight around the airframe tube, moreover, they’ll be suceptible to cracking as the rocket is handled during building.

To effect repairs, I used a little bit of foam-compatible CyA and a fair amount of epoxy clay. In particular, I used the epoxy clay to fill all the gaps, and a slurry of epoxy clay thinned with 90+% isopropyl alcohol to fill the cracks. Tedious, but it seemed to work well. Most of the time, I resorted to using a hobby knife as a spatula to apply the slurry.

Fin fairing base damage.

Repaired fin fairing base.

It was more than just the wraps that were damaged. Over the years, the wooden base form of one of the fin fairings had broken. I decided to remove the detritus, essentially breaking it further (this is shown to left) and then cutting out and gluing in a new base piece.

The fin fairing wraps are particularly delicate: there’s not much behind them except air, and it’s very easy to break them. In addition, they have to be glued down while under stress, since the curvature of the wrap almost certainly isn’t exactly right. This makes it particularly easy to crack or melt the fairing wraps. This model suffered from some of both, cracked fin fairings and melted fin fairings. A picture showing one of the repairs is on the left.

Fin fairing damage, repaired.

Additional ullage rocket.

AS-501 had eight ullage rockets on the S-IC/S-II interstage (as did AS-500F [the facilities checkout vehicle] and AS-502 [aka Apollo 6]). The Apogee kit comes with four ullage rockets molded into the wrap, which is correct for AS-503 (Apollo 8) through AS-509 (Apollo 14). On the right, you can see one of the extra four ullage rockets I added to this model.

As I did on the AS-510 model, I filled the spirals in the airframe body tube to give things a more finished look. This committed me to a lot of sanding (for which maybe I should have been committed!), but the end result will be much nicer. I admit that I didn’t do a grade A job of filling and sanding, in part because I really want to get this done in time to launch if we can fly in April.

Spirals filled.

Spirals sanded; ready for primer.

Pictures left and right show the spirals before and after sanding. Below center, you’ll see that same area after the first coat of primer went on.

Following that first coat, I sanded, and applied another coat. After sanding that, I decided it was time to paint. But first, I took care of the broken fins, removing their roots, and those of the other fins (which were damaged), with a plan of just replacing all four fins. Some touch-up priming, and it was painting time.

After a coat of primer.

Below you’ll see the current state of affairs: the rocket has its base white paint on. Next up: masking, and then painting a slightly off-white (pseudo-weathered look), to get the right look for AS-501 as it was ready for launch. Then, more masking and painting the black roll pattern, along with some final research on the CM radiator panel configuration and paint scheme.

(What about rocket building? Very much underway. Too busy working on BAAH-1, my L-1 certification project, actually to write up the progress. But, I’ve taken lots of pictures. Quick summary: airframe done, fins painted and attached, motor mount complete, nose cone painted, rest of airframe primed and ready for final sanding and paint.)

This past Saturday, NASA’s Ames Research Center—all but next door to where I live—hosted an open house to celebrate its 75th anniversary. What a wonderful idea: get the public in, let them see what’s going on at NASA today. And the public was certainly interested: something around (probably in excess of) 100,000 people came to the research center. There were long lines to see what was set up outside the various buildings along the self-guided walking tour.

Long lines. To see some posters and some medium-screen TVs with the sound turned down. Inside inflatable pseudo-mock-ups of the approximate ISS interior section diameter. To see a section of the Orion developmental heat shield, at full scale, propped up to view. To see the outside of the 40×80 and 80×120 wind tunnels. And to try to get through to the opposite side of the center when the single open road connecting areas was closed because of a medical emergency, and no alternate route was opened.

NASA blew it. NASA blew it badly.

Here they had the chance truly to excite people, to inform them, to educate them, to get them enthusiastic. And they squandered the chance.

Take the Orion heat shield exhibit. They could have had ten identical stations set up, in a big circle or square, so lots of people could see at the same time. They could have had blow torches aimed at each heat shield section, controlled by someone (or one someone per station). They could have had thermometers with big displays showing the temperature on each side of the heat shield section as the blow torch’s intensity is varied. Or they could have had one such station with a bunch of big TVs, so lots of people could see at the same time. Now, this static thing that’s interesting to engineers and space geeks becomes this very cool stuff with an obvious demo.

Take the 80×120 wind tunnel. It’s the biggest wind tunnel in the world. A few people—special ones with magic “back stage passes”—could get inside the 80×120, but we poor peons couldn’t. If you didn’t know what the thing was, there was scant little info available. Why not set up a bunch of big screens around the thing (it’s 120 feet wide, after all—and that’s the test section, not even the even larger exhaust outlet!) with staff and volunteers and 30 second video clips of actual tests running in the tunnel—tufted string tests and smoke wisp tests, and explanations of the supersonic parachute deployment test video they had (that was looping with perhaps ten other tests)—so people could see what’s going on?

How about plans for alternate routes through the center in case a road has to be closed? (It would have been trivial to have the security people change the barricades around.)

How about some astronauts—not just one, but a dozen—circulating, or scattered around the grounds, talking with people about what it’s like to be in space, aboard the ISS, to ride the rockets? Talking with people about why people have to be up there, people have to be exploring? Robots and orbiters and rovers serve important purposes, but people still have a place in space—what’s that place, and why is it important? Get astronauts who are photographers and poets and painters and authors and great speakers to talk about these! (We do not need send different people for this: we’ve already sent astronauts with all these hobbies and qualifications into space.)

NASA and Ames, stop thinking like scientists at scientific meetings, and start thinking about market to the public, about selling the incredible, cool stuff that you’re doing—in space, here on earth; for space exploration, for planetary exploration, for terrestrial exploration, for solar exploration; on spacecraft development and aircraft development and watercraft development; to examine the human condition; to enrich humanity.

It was a great day at the ranch! (Many thanks, again, to Bill Orvis and his family for allowing us to fly on their ranch!)

The temperatures were moderate: not hot, certainly not cold. In the sun, it was pleasantly warm. The winds were very light. The sky was clear. It had rained lightly—just enough—a couple of days before, so the fire danger was minimal. Many of us were really itching to get out to fly on the grass, to fly high, to fly big, just to fly.

On Thursday evening, I checked my inventory and decided what to bring; Friday evening, I loaded up the car and got a mobile breakfast ready. I planned to fly 4TNC (“4 Tubes and a Nose Cone,” a take-off on the stereotypical 4FNC [or 3FNC]—4 Fins and a Nose Cone—denoting the simplest of model rocket configurations) and Die Fledermaus, and also took Krystal (though I figured it unlikely I’d fly her) and my venerabl 50+ flight Alpha III. This was to be Die Fledermaus’s first flight since the crash. That crash, on her second flight, was not serious, but some creek bed stones punctured the airframe. Though I have not finished sanding out the patches, much less painting them, I decided it was time to fly.

I flew 4TNC a couple of times, to get things started easily. B6-4 on the first flight, C6-7 on the second. Both nice flights.

First flight: G64-4W. The rocket arced off the pad a bit more than I wanted, but it was a nice, pretty flight with white smoke against the blue sky’s background. The rocket landed across the creek, about 80 or 100 meters north of the flight line. Second flight: another G64-4W. This flight went straight up, and was still clawing for the sky when the chute deployed: a 7 second delay, though perhaps too long, would have yielded a higher maximum altitude. Again, landing was a bit north of the flight line, perhaps 50 or so meters. Both flights hit 200 meters.

I arrived at the Ranch about 10am. It was good to see folks again. And we all agreed that morning to a paraphrase of Col. Kilgore.

Most of the recent work has been on BAAH-1’s paint prep. Not quite all, but most.

The balsa nose cone takes an enormous amount of work to get it as smooth as I want it. I don’t need a polished hardwood furniture-grade finish on it, but I don’t want all the lathe pits and typical balsa deep gouges filled. I’ve been using Pactra balsa filler coat and diluted Elmer’s wood filler, with a healthy amount of elbow grease and sandpaper mixed in. At left is the nose cone in filler coat.

I felt that the balsa wood of the nose cone would not be as strong as I wanted for retaining the recovery harness U-bolt. I decided to attach the U-bolt to a bulkhead, then epoxy and glue the bulkhead to the base of the nose cone. Though this would add weight, it would be much stronger, I felt. The picture at right shows the nose cone and its baseplate assembly, with the whole thing in a clamp mechanism. (Note that I changed from the balsa filler coat to the diluted wood filler between these two pictures.) To get everything to fit flush, I had to remove some of the base of the nose cone, in order to provide a channel for clearing the U-bolt mounting hardware.

The final result of the baseplate addition, along with another coat of wood filler, is shown in picture below right.

I really do want the finish on this rocket to be nice. I’m going as far as borrowing a technique from my Saturn V: filling the spiral wind grooves in the airframe tubing. See the blog entry from mid-May 2009 (“Primed!”) for a picture of this (both before priming and after, for a quick comparison). There’s an incredible amount of sanding needed to get everything smooth, but I figure it’s worth it. Besides, I’m modeling a smooth surface with no spiral winds, and if I’m going to the trouble of ½” eye bolts for launch guides in order to be historically accurate, I’ll certainly fill the spirals, and get the nose cone looking somewhat nicer than balsa (I’m modeling a wood nose cone, so it needn’t be perfect, but it takes a lot of work to get balsa even close to smooth!).

As to those eye bolts, I realized I had another problem with the launch guide issue. I had one eye bolt near the forward end of the rocket, and one nearly fully aft. Once the forward eye bolt left the launch rod, the launch guidance was gone: nothing would keep the rocket aligned, since the eye bolt can pivot, at least a little, around the rod. The only solution, while still maintain what I’ll call historical mission accuracy (i.e., launching off a rod, not a rail) was to add something well aft to maintain alignment. I decided to add the capability to install additional eye bolts during launch prep. By going to three eye bolts at the aft end, I was essentially building a launch lug assembly. Unfortunately, with the motor mount now fully installed, accessing the area for the backing nuts for these two eye bolts was difficult. Possible: they’re aft of the mid centering ring. But difficult.

Blind nut for forward eye bolt, with conformal washer

Backing assembly for the forward launch guide eye bolt.

Below left is a a backing nut assembly for the aft eye bolt launch guide. As with the previously-installed launch guide backing nuts, I wanted a roughly-conformal surface for the epoxy between the assembly and the body tube. I used some epoxy putty to secure things, and could then epoxy the assembly to the inside of the airframe. You might wonder why I used the odd-shaped nut. Because I had already installed the motor mount, I knew it would be a challenge just to get the assembly properly positioned and held while I secured it (I screwed it down with a ¼”-20 machine screw and a jam nut on the opposite side of the airframe wall). I happened to have both the oddly-shaped T-nut and the similarly-shaped washer, and they seemed to fit the bill nicely, giving me the right sort of surfaces for grabbing with needle-nose pliers while holding it in place and securing it. On the right, then, is a picture of the assembly in place: you can see just how tight a space that is.

What about the forward eye bolt? It was straightforward: curve a regular stainless flat washer, epoxy a stainless nut and washer together, let them cure, then epoxy the assembly to the inside wall of the airframe. I used the same positioning technique as described above.

On to the fins!

Fins in the paint jig, ready for priming.

First couple of coats of primer complete.

The picture at left shows the fins before priming; on the right, after a couple of coats of prime have been applied. I’m not certain how many primer coats I’ll end up using.

The jig holding the fins upright for painting is the front of a dresser drawer that I salvaged from somewhere: I don’t recall where. The groove in the drawer front happens to be just about a perfect fit for the fin tabs with some tape to mask them off. Pure happenstance, but I’ll take being lucky when I can can get.

It happened to be a nice warm day for this time of year (March 2013!) that Saturday afternoon when I was able to prime. Just about perfect conditions for painting, though I would have preferred a little less breeze.

…

It’s now nearly a year after I first drafted this, nearly a year of inactivity on the blog (other than the posting about the February LUNAR Snow Ranch launch!), nearly a year’s hiatus in building BAAH-1. Other aspects of life have intruded, not all of them bad (e.g., a wonderful family vacation to Alaska!). Soon, it will be back to the Rocketworks and BAAH-1.

The nose cone is a reasonably nice plastic cone, sized, at least roughly, for high-power tubes. They’re probably just about perfect for what appears to be the standard 2.56″ (65.0 mm) I.D. and 2.63″ (66.8 mm) O.D. tubes, with a 0.035″ (0.89 mm) wall thickness. I’m using Blue Tube (from Always Ready Rocketry), though. The I.D. of Blue Tube is standard, so things like nose cone shoulders, centering rings, and bulkheads will fit just fine. But, the wall thickness is nearly double a conventional high-power tube, at 0.062″ (1.57 mm). The shoulder of the nose cone fits just fine, but there’s a lip between the top of the tube and the nose cone: the edge of the nose cone sticks out.

The plastic nose cone is just a little bit too small.

It would be easy enough to sand down the nose cone (assuming the wall isn’t compromised!). Sanding down the body tube, ideally tapering it in some nearly-imperceptible way, is another thing, though.

I decided to get a new nose cone. Bill Saindon of Balsa Machining Service was very helpful in this regard. I measured things very carefully, and sent him the specs of what I wanted (this-and-such should diameter, that-and-such diameter of the nose cone body; he has some standard shapes, one of which seemed just right). I sized the new nose cone to be about 0.003″ over the tube diameter, knowing I would be sanding it smooth.

When it arrived, it fit perfectly. I’m now sanding, filling sanding, filling, sanding, and filling some more to get a nice, smooth finish.

Post Scriptum: Bill is no longer providing semi-custom balsa machining services. My order was in transit when I learned of this change, and I talked with Bill. I am very grateful that he made my nose cone: it was his last semi-custom job.

And the grandaddy of all rocketeers’ clichés: Okay, Houston, we’ve had a problem. (This one is famously mis-quoted.)

The problem is hardly as life-threatening as that experienced by Lovell, Swigert, and Haise. It didn’t take as long to fix, nor did I have to be as creative as those in Houston to solve the problems facing that crew.

First, some of what’s occurred since my last post on BAAH-1.

The forward centering ring, clamped and glued.

Close-up of the forward centering ring, glued and clamped.

Finding the right U-bolt for attaching the recovery harness to the forward CR wasn’t quite trivial. That ring is pretty narrow: the MMT is 38 mm, the airframe is about 65, resulting in the CRs being only about 13 mm wide. Finding a U-bolt that fit inside the airframe and outside the MMT, with mounting hardware (washers and nuts) that clear the MMT and the airframe, and providing enough strength that I’m happy with the affair, and, ideally, made of stainless (since it will be exposed to the ejection gases and completely inaccessible once the rocket’s built, because of depth in the airframe) took some work. Eventually, I found a 4 mm stainless U-bolt at a marine supply company.

As I pondered the situation, I came to feel that the CR might be a little on the thin side to be as strong as I wanted. I happened to have an extra CR, so I decided to double the ring. Almost certainly overkill…

At left and right are pictures of those two rings glued together and clamped for drying, to form the forward CR and recovery harness anchor point. In order to avoid putting a big dent in the final CR, I grabbed some scrap wood to use between the C clamps and the CR, with a little wax paper in strategic places just in case some glue somehow seeped out. I cut down some extra length on the U-bolt legs, too, after the glue dried.

The mid centering ring epoxied in place, epoxy setting.

Hex nut to secure the aft launch guide.

Next up, install the mid CR on the MMT. Again, a little wax paper helped ensure I didn’t epoxy the whole assembly to the vice that held the MMT upright while the epoxy set.

Time now to unknowingly create the beginning of my problem.

The plan all along, carefully thought through, has been to insert the MMT from the aft end of the rocket, use the aft CR to align things long enough for me to install the forward CR (but not yet epoxying the aft CR in place), then let the epoxy set with the rocket upright. If I applied the epoxy correctly to the inside of the airframe, this would provide fillets in the two areas I would be unable to access once the MMT was installed in the airframe. To do this successfully, I needed to install the hex nut securing the aft launch guide after installing the MMT, even though reaching in between the MMT and the airframe would be difficult. I even included this in the build guide I wrote for myself.

Did I refer carefully to the sequence of steps in the build guide? Nope. While the mid CR’s epoxy was setting, I installed the hex nut for the aft launch guide. I think I did a nice job, bending a washer to conform to the curve of the airframe’s inner wall, getting it placed and epoxied without gumming up the threads, etc. Only problem was that the nut now blocked installing the MMT in the way I had planed.

Feh.

I didn’t realize the problem immediately. Instead, I set out working on other tasks while all this epoxy set. These tasks included, among other things, attaching the recovery harness to the forward CR’s U-bolts. This, too, presented some small design issues. I have a nicely woven piece of Kevlar® to run from the anchor point to the parachute’s quick link. The Kevlar has a loop sewn in each end. The loop doesn’t fit over the double U-bolt system, and a quick link big enough to go between the U-bolts for the Kevlar sewn loop would be very large. I didn’t want to skip this double U-bolt system.

Close-up of the shock cord harness mount.

I have some ½” woven Kevlar cord, so I made a harness adapter, using a blood knot to make a loop that goes through everything. (The ends are dressed with heat shrink tubing, to keep them from unraveling—probably a vulnerable point in the whole harness—and dressing the ends with some thin Kevlar cord.

All set. Time to install the MMT, including the forward CR.

This is when I discovered the problem of that hex nut blocking installation of the MMT assembly.

At least I realized the problem before I mixed up the epoxy (much less, applied it to the airframe!). There was a chance I could work around the problem, though I wouldn’t have that optimal filleting: just insert the MMT assembly from the forward end of the airframe. In order to be able to get the epoxy applied inside the airframe for the forward CR, I would apply the epoxy and slide the forward CR onto the MMT after inserting the MMT assembly and positioning it. I tested this out in a couple of dry runs, and it seemed like it would work fine.

But, it didn’t.

Initially, I thought it had worked. The MMT assembly went in just fine, it ended up in the right position, and the forward CR’s epoxy and installation went without apparent problem. After filleting the forward joint between the airframe and the forward CR, I examined the installation carefully, peering waaay down inside the airframe, as I got ready to filletand clearly saw that the forward edge of the MMT was not visible beyond the CR. In fact, I could see what I thought was a lip. I little probing with a long rod confirmed this. The epoxy equivalent of a cold joint on a circuit board. I thought about this, tried to push the CR down, jiggling the MMT a bit hoping to improve the alignment (in case that was the problem), and realized I couldn’t budge that CR.

I set everything to cure, pondering the problem overnight.

The “cold joint” between the forward CR and the MMT.

I thought about leaving everything alone, figuring that, perhaps, the CR-airframe joint would be strong enough to hold everything together, and the two CRs around the fins would keep the MMT secure. I decided I wanted to get this right.

I thought about dumping enough epoxy into the cold joint to bond the ring to the MMT, using a stick or rod to get the epoxy down to the joint.

I thought about cutting the airframe several centimeters forward of the ring, so I could look at the joint, then reassembling the airframe with a tubing coupler at the joint when the repair was complete.

I decided I should cut and repair the airframe.

Out came the miter box, open came the airframe (cutting carefully: I had to cut around the airframe, not straight through it, unless I carefully tucked the lower portion of the recovery harness deep into the rocket). The pictures show the situation, first before, then after repairing the cold joint. They don’t tell quite the whole story, unless you have a very sharp eye (or examine the full-size pictures carefully). Rather than simply throw epoxy into the cold joint, I started thinking about other options. I had cut the MMT down (initially, about 120 cm, using 75 cm in the rocket, to ensure adequate room for the parachute and any avionics bay I might install later). This left me with a nice piece of 38 mm MMT tube; I also happened to have an appropriately-sized tubing coupler, even though I didn’t expect to need it. What about, then, using the coupler and a small piece of the 38 mm tube to extend the MMT out through the forward CR? This seemed like a good option, but I wanted others.

I also considered just using the tubing coupler, without adding the 38 mm tube. This had the advantage of not having to fit the 38 mm tube inside the hole in the CR, which might have proven difficult given the slightly flawed alignment. It would also be easier to get the coupler into the CR than to get the larger 38 mm tube into it, since the coupler was slightly smaller.

Repair of the cold joint between the forward CR and the MMT.

I decided on using just the coupler, and to apply enough epoxy to fill the gap between the coupler and the CR. This would also provide a good, solid fillet.

The picture at left shows the result. It looks like the repair turned out pretty well.

Last bit of the repair: reassemble the airframe. That was pretty straightforward, since I had an extra coupler for the airframe tubing. The picture below shows an intermediate stage of this portion of the repair: the coupler’s epoxied into the lower segment of the airframe, and the protruding portion of the coupler has epoxy applied, ready to be joined with the upper portion of that airframe tube.

I also took the opportunity afforded by access to the lowest portions of the recovery harness to add a Nomex® shock cord protector. This is the darker yellow sleeve around the shock cord, secured by some Kevlar cord. It’s not complete protection for all the lower portions of the harness, since the ½” inch Kevlar loop through the U-bolts is unprotected, but it’s still better than it was before.

Remaining in this bit of the repair: fixing the cosmetic damage inflicted by sawing the tube in half. I’ll do that when I fill the spirals in the airframe tubing, prior to painting.

The maiden launch of Die Fledermaus was on Saturday, February 2nd, at LUNAR‘s Snow Ranchlaunch facility. It was a beautiful day: light winds, pleasant temperatures, a good turnout of fellow space cases. Perfect situation to fly Die Fledermaus.

The first flight, on a G64-4W, was fabulous. Picture-perfect. Nice, straight up, ejection near apogee, gentle landing not far away. The flight made 200 meters, 35 meters below simulation prediction. (I did not weigh the rocket before flying, so the build mass is probably a little more than the design mass.)

The parachute fouled on its shroud lines, and did not fully inflate. It could catch some air, sure, but a parawad on an Estes Alpha III from 50-70 meters and a parawad on a 1 ½ kg rocket from 200 meters are two different ballgames. It wasn’t a catastrophic crash, but the rocket certainly hit the ground faster than the design of ~4 ½ meters/second. The bad news was not exhausted, though: it landed in the creek. Hundreds of acres of ranch, light winds, and the rocket ends up in the creek.

The water wasn’t a big problem: with the help of a friendly fellow rocketeer, Die Fledermaus was partially dunked for well under a minute. But, like many, many small creeks, the bed was strewn with rocks and stones. Die Fledermaus hit a few on the way down, with the damage shown below.

In the airframe damage picture, notice the smudge and cracked paint on the right side of the picture, above the second “e.” That looked like bad news. The saving grace: it’s right on the MMT’s forward centering ring, so there’s apparently no significant weakening of the airframe.

Last night, while working on BAAH-1, I had some extra epoxy (JB Weld, truth to tell) mixed up. Rather than just let it harden and go to waste, I applied some of it to the damage to begin repairs. There’s enough of the airframe left to serve as supports for the epoxy patch (initially, I thought I might have to back the big hole with some cardboard, just to hold it in place).

At the right are pictures of the repair. The outer surfaces will need sanding and painting, but she should fly again!